OutlookStatView from NirSoft is a freeware utility that you can use to scan your Outlook mailbox and retrieve some general statistics about the users you communicate with.

It will separate your frequent contacts by the number of outgoing messages you sent to them, the number of incoming messages you received from them, the total size of messages sent by the user, the email client software they used and the time range you send/received emails from specific users.

The tool will work on any version of Windows between (and including) Windows 2000 and Windows 7.